Combustion apparatus for an air stream and propulsive system



M. L. NATHAN May 12, 1953 COMBUSTION APPARATUS FOR AN AIR STREAM AND PROPULSIVE SYSTEM 2 Sheets-Sheet 1 Filed Sept. 5, 1945 May 12, 1953 M. NATHAN COMBUSTION APPARATUS FOR AN AIR STREAM AND PROPULSIVE SYSTEM 2 Sheets-Sheet 2 Filed Sept. 5, 1945 Patented May 12, 1953 COMBUSTION APPARATUS FOR AN Am STREAM AND PROPULSIVE SYSTEM Matthew Lewis Nathan, Godalming, England, as-

signor to Power Jets (Research & Develcpment) Limited, London, England Application September 5, 1945; Serial No. 614,503

InGreat Britain March 16, 1944 Section 1, Public Law 690, August 8,19 46 f quired, and where the pressure loss due to mixing and combustion is to be kept to a minlmum although the volumetric space available is restricted. Such a case (and it is primarily to meet the requirements of this case that the inven-' tion is conceived) is that in which it is required Patent expires Marclr'16, 1964 11 Claims. (Cl. 60-'35.6)

to burn liquid fuel in, an air stream which has I been'generated for the purposes of aircraft propulsion, in a'duct which forms part of a jet propulsion or ducted fan system. In a particular example to which the invention is proposed to be applied, and which is included in the invention, there is in an aircraft propulsion system, a gas turbine prime'mover which by its propulsive exhaust drives an augmentor turbine which in turn drives an axial-flow compressor, the air energised by this compressor forming a thrustaugmenting stream in an annular duct surrounding the exhaust stream from the prime mover.

In the augmentor stream, downstream from its compressor, fuel is to be burnt to energise this stream further. In such a scheme, it is necessary for practical utility that this secondary combustion should occur with the least possible pressure loss, whilst it will be clear that consideration has also to be given to space and weight.

Furthermore, while on the one hand, the combustion of a jet or spray of fuel in an air stream is best effected in a cylindrical combustion chamv her, on the other hand a chamber which is whol' ly cylindrical does not make the most efifective which their general directions are substantially. parallel within a common annular duct, each of the said flame tubes comprising a partially obtu- Fig. 3 is a left hand end view of said embodiment;

Fig. 4 is a sectional view on the line 44 of Fig. 2; I

Fig. 5 is a perspective view of a detail;

Fig. 6- is a section on the line 6-6 of Fig. 1.

Referring to the drawings, Fig. 1 shows the general arrangement of a propulsive system for aircraft to which the invention is intended to be applied. This system comprises a compressor rotor I driven by a gas turbine 2 mounted coaxially on the same shaft, the air drawn in by the compressor being brought to combustion together with fuel in the compressor output which is delivered to the combustion chambers 3 in which combustion takes place. The hot gases are led through the turbine 2, thus driving 7 it, are then passed, through an annular duct 4 and are finally emitted through an outlet 32 forming in this way a main propulsive jet stream.

The propulsive system further comprises an augmentor system 5 comprising a further gas turbine element 6 which in turn drives a further compressor or ducted fan I which entrains new or secondary air through an annular duct 8.

; This air passes along the duct 8 and finally emrated upstream end and a wall pierced for the Y inward passage of air, each tube being associated wise. a I,

By way of example, one'form of embodiment of with a downstream outlet which is formed sectorthe invention is describedhereinunder with ref erence to the accompanying drawings in which: Fig. l is a general representation partly in longitudinal section of a system in which the invention is intended to be applied; Fig. 2is an enlarged view in longitudinal-section of one form of embodiment of the'i'nventior'i;

ergesfrom the apparatus at the outlet 33being expelled together with the main jet stream from the outlet 32 and thus augmenting the thrust produced.

Downstream from the augmentor 5 in the secondary air, secondary fuel is burned in a number of flame tubes 9 arranged in the annular duct 8 to augment the thrust by raising the velocity of discharge, fuel being injected into the flame tube 9 by means of a burner It. The end of the duct is shown in section, to reveal the flame the flame tubes9. f

The invention is concerned with. the construction and arrangement of the flame tube 9 and an enlarged view of such a flame tube in longitudinal section is shown in Fig. 2.

The flame tube consists mainly of a light sheet metal cylindrical body II with apertures l2, l3, distributed axially and circumferentially for the inward passage of air. The upstream end of the flame tube is slightly reduced in diameter and is provided with a conical obturator M which has tangentially directed air pockets ll (Figs. 3 and 5) to receive and swirl primary air in the region of an atomising burner lilwhich is fitted the obturator M.

of the member l4, it may be referred to as a primary swirler.

The swirler I4 is more clearly shown in Figs. 3 and 5. This is hexagonal in form and. comprises six pockets ll arranged around the periphery and, each [provided with a triangular. opening I5; the walls IQ of the pockets ll being 5 arranged so that air which is travelling in the direction of the arrow P in a plane perpendicular to the plane of the paper in Fig.; 3- enters.{the opening l5 and is then deflected through apprpximately 90 into the plane of the paper in Fig. 3, 1O travelling through the pocket H and finally emerging from said pocket through a narrow-rem tangular aperture l8 whereupon the air strikes the wall IQ of the immediately adjacent pocket and is then obliged to travel in the direction oi- 15.

the arrow Q by reason of its impaet against said wall 19. By the provision of a numberot such; pockets I! in the swirler [4, the air is inducedto follow a rapid swirling motion as show n -by the arrows in Figs. 2 and 3, the vfull line arrows indicating ,the, air, before, it enters the. pockets I! and the chain line arrows indicating the path of the a ir aiter it has emergedjrom said pocket.

As above mentioned, the pockets H are provided for the.;admis sion,oi' primary .air audit is advantageous to maue these pockets L as large as' possible. while airis alsoadmittedtothe flame tube 8 around theoutside of ,the primary swirler,,.. I4 throughthe six sectionalgaps 2 I vmadeby the v junction ,of the hexagonal swirler H with the circular fiametube body ll., Tlii assists. greatly inreducingthe combustion pressure;;loss, while thelstrong swirl imparted to.;the. portion of the primary air neartheaxis of thepflame tube ,9, as shown bythe.,feathe red arrows at K. inf'ig z 5 creates sufficientreversal to hold the name,ipackon tothe-burner 10 at .very lowf uel flows. This I reversal is also fedby airadmittedto the-central 3 region .ofthe flame tubethrough two tubesijz which cross, substantiallyhat right angles at a 40 suitable distance, for exarnpleaboutsmf down: stream of the ,burnerd 0.. .,These, tubes}? are pro; v vided with lateral apertures 29 cnthei-rnpstream side and, with inclined openings 31!, at each end which face upstream. Additional, prima1y air ssn e s t tubes". an .fl9 QWar is-h i'e ra in ssie by e e rQwsX s m -ia 2 incthis additional primaryv air; assists; in pbtaining stable combustionv at wery. rich mixtures.

The two cross tubes 22 also impart rigidity to the flame vtube body. U

Secondary is dmit edi thefl met efli u h a W .of l n u n l t 1 amiamt-n of longitudinal slotsl.3.} The.slotsSiZ are asso ciated with nozzles 2 3, and have, been iound eff ficient in introducingairto the central praxial region of the secondary; combustion zone as shown by the arrows Y, and the imprgyedmixing thus obtainedgiyes, more I complete, come bustion at rich mixtures,

The downstream end of the flame tube .9 changes its section smoothly from circular at the portionll to segmentalat the portion leaving, an annular passage l d-between the end z t of the flame t a the du t l s 1.21 irQmWh h passage issues a stream of relatively coolair oi even thickness in the directionof the arrowsl which stream is interposed between the hotcornbustion products and theduct walls 2f! thusk eeping the'latter cool while-at" the same time the 7 outlets 26 together occupy substantiallythe whole of the annular section of duct 8; This aircons titutes tertiary airand gradually mixes with the products ofcombustion in the regionbetween the end li er the flame tubes 9 andt -nn gs ejection nozzle 33 at the same time keeping the duct wall 21 upstream of said nozzle reasonably cool. Each flame tube 9 may have an electric spark igniter; plug .35 extending into ;it through theopening at (For only one or some selected ones of the series is provided with such means, in the latter case all flame tube being interconnected by -lateral, pipesthrough a union 3| to enable one flame; tube to light up from its neighbor.

The burner l0 injects fuel into the flame tube 9 through a nozzle 20 which may produce a single jet; or aplurality offuel jets.

The-'dimensions-of the flame tube 9 are different frqm the hitherto known tubes in that while-maintaining the same length, the width of mi sn ma-ry. seco dary a d t t r a r in the desiredquantities and; proportions.

The fl wof cold air and hot gases. through the fi meii be ndic te b ar w e ath ed arrows (indicating hot gases and the non feathered arrows indicating cooler, air.

It is convenient to arrange ior a series of for m e n. fl me t be .t e t nd c m let l e q nsl e mfer nce 0f thed i Bra sh wn.

in Fig, 6. Each fiametubefi may itself be proed w h a segmental casin andtmsuch ee: mental casingsmaythen be arranged ,to occupy ecom l te c mfer neecf ed .B,

. I l im;

1. Combustion apparatus for burning iueiin M an air-stream comprising, a combustion chamber.

in the form of an an nular, duct f.or said stream,

andfla plurality 0f.fiame ,t ubes arranged as a circula series within saidductwith their lengths,

substantially parallel to the axisof the duct, said flame tubes beingmadeup of partiallyobturated upstream ends apertured to admit primary air,

perforatedparts of circular. cross-section extend;

ing from said ends, of such diameter that together I they occupy almost thefull width and fullv mean circumferencepf said, duct and downstream out-..

let ends discharging into said annular, duct said outletends being of sector-shaped section into which said circular. parts smoothly merge, all the sector-shaped outlets together I occupying sub- I stantially a complete annular section of said,

2. Combustion apparatus for burning fuelin.

an air stream, comprising a combustion chamber in the formof an annular duct for said stream, and a plurality of flame tubes, arranged as a circular series within said duct with their lengths substantially parallelto the axisof the t s id fl mefi e be mad n p ti lly,

obturatedupstream end walls apertures to ad mit rimar air perforated cylindrical walls extending from said end wallsto form upstream partsof circular cross-section, downstream extensions of said walls iorming outlet ends. of sector-shaped section, into which said circular parts smoothly merge, and at least two nonparallel inlet tubes extending through the said cylindrical wall of each saidflame tube for ad mittingadditional primary air to the interior of U the flame tube, said circular upstream parts being of such diameter that together they occupy almost the full width and mean circumference of d duct- .w le. Sa d.,.S, 0 Ql'?$haD. d. .,o 1 s. w qhdisghereei p sa uetrjoe ther. occ rs.

substantially a complete annular section of the duct.

3. Combustion apparatus according to claim 2 wherein said inlet tubes, which are two in number, are arranged substantially at right angles to one another within each flame tube and provided with a plurality of lateral apertures on their upstream side.

a. Combustion apparatus according to claim 2 wherein said inlet tubes, which are two in numher, are arranged substantially at right angles to one another within each flame tube and provided at each end with openings passing upstream for the admission of primary air and with a plurality of lateral apertures on their upstream side.

5. Combustion apparatus according to claim 2 wherein said inlet tubes, which are two in number, are arranged substantially at right angles to one another and provided with a plurality of external apertures facing upstream and at each end with openings facing upstream for the admission of primary air, each flame tube further comprisin means for admitting secondary air downstream of said inlet tubes.

6. Combustion apparatus according to claim 2 wherein said inlet tubes, which are two in numher, are arranged substantially at right angles to one another and provided with a plurality of lateral apertures facing upstream and at each end with openings facing upstream for the admission of primary air, each flame tube further comprising means for admitting secondary air downstream of said inlet tubes, at least some of said means being adapted to direct the air within the flame tube.

7. Combustion apparatus according to claim 2 wherein said inlet tubes, which are two in numher are arranged substantially at right angles to one another and provided with a plurality of lateral apertures facing upstream and at each end with openings facing upstream for the admission of primary air, each flame tube further comprising means for admitting secondary air downstream of said inlet tubes and means for admitting tertiary air into the space between the external wall of each flame tube and the internal wall of said duct, at least some of the means for admitting secondary air being adapted to direct the air within the flame tube.

8. Combustion apparatus according to claim 2 including inter-connecting tubes extending laterally between said flame tubes and wherein said inlet tubes, which are two in number, are arranged substantially at right angles to one another and provided with a plurality of lateral apertures facing upstream and at each end with openings facing upstream for the admission of primary air, each flame tube further comprising means for admitting secondary air downstream of said inlet tubes and means for admitting tertiary air into the space between the external wall of each flame tube and the internal wall of said duct, at least some of the means for admitting secondary air being adapted to direct the air within the flame tube.

9. Combustion apparatus for burning fuel in an air-stream, comprising a combustion chamber in the form of an annular duct for said stream, a plurality of flame tubes arranged as a circular series within said duct with their lengths substantially parallel to the axis of the duct, said flame tubes being made up of partially obturated upstream end walls apertured to admit primary air, walls extending from said end walls to form 6, firstly upstream parts ofcircular cross section occupying together almostthe full width and mean circumference of said duct and secondly downstream outlet ends of sector-shaped section into which said circular upstream parts smoothly merge, the sector-shaped outlets, which discharge into the duct,'together occupying substantially a complete annular section of the duct, an electric igniter in at least one of said flame tubes, a plurality of inter-connecting tubes extending laterally between said flame tubes so that the interior of every flame tube without an igniter is connected to the interior of at least one flame tube provided with an igniter as aforesaid, and, for admitting additional primary air to'each flame tube," two inlet tubes extending through the wall of said circular upstream part of each of said flame tubes substantially at right angles to each other, each said inlet tube being provided with a plurality of lateral apertures facing upstream inside the flame tube and at each end with openings facing upstream for the ad mission of primary air, each flame tube further comprising means for admitting secondary air downstream of said tubes and means for admitting tertiary air into the space between the external wall of each flame tube and the internal wall of said duct, at least some of the means for admitting secondary air being adapted to direct the air within the flame tube.

10. A propulsive system comprising a first air compressor, means for burning fuel in the output air from said compressor, a first turbine driving said compressor and driven by the gases of combustion, an axial flow compressor, an augmentor turbine driven by at least part of the exhaust gases from said first turbine and itself driving said axial flow compressor, a duct for the passage of the exhaust stream from said augmentor turbine, and having a reaction propulsion nozzle, an annular duct surrounding said exhaust stream for the passage of a stream from the axial flow compressor and having a second reaction propulsion nozzle, and in said annular duct combustion apparatus comprising a plurality of flame tubes arranged as a circular series within said duct about an axis with which their general directions are substantially parallel, each of said tubes being associated with a sectorshaped downstream outlet and having a partially obturated upstream end, a swirler for the admission of primary air towards said end, and a wall pierced for the inward passage of gases, each swirler defining by its outer boundary surface in combination with the adjacent internal surface of the flame tube within which said swirler is arranged a plurality of separate openings located between said surface and comprising a. plurality of tangentially directed pockets mutually cooperating to deflect the air passing therethrough and to produce a turbulent motion on the air issuing therefrom.

11. Propulsive system comprising a first air compressor, means for burning fuel in the output air from said compressor, a first turbine driving said compressor and driven by the gases of combustion, an axial flow compressor, an augmentor turbine driven by at least part of the exhaust gases from said first turbine and itself driving said axial flow compressor, a duct for the passage of the exhaust stream from said augmentor turbine and having a reaction propulsion nozzle, an annular duct surrounding said exhaust stream for the passage of a stream from the axial flow compressor and having a second reaction" propulsion nozzle, and in said" annular duct combustion apparatus comprising aplurality of flame tubes arranged as a circular series within said duct about an axis With which their general directions are substantially parallel, each of said tubes being associated with a sector shaped downstream outlet, and all the outlets together occupying substantially a complete annular section of said duct.

MATTHENV LEWIS NATHAN.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Lubbock et al. Sept. 30, 1949 Number Re. 23,149

Number 8 Name Date Todd et a1. Oct. 26, 1909 Avery Mar. 7, 1935 Hammer Nov. 19, 1940 Lubbock Apr. 16, 1946 Davenport June 18, 1946 Whittle July 16, 1946 Whittle July 16, 1946 Way Aug. 13, 1946 Whittle Aug. 13, 1946 Streid Dec. 9, 1947 Halford July 13, 1948 Wayet a1 May 6, 1952 

